IgG4-related epididymo-orchitis associated with bladder cancer: possible involvement of BAFF/BAFF-R interaction in IgG4-related urogenital disease.

We describe herein a patient who presented with immunoglobulin G4-related disease (IgG4-RD) involving the testis and prostate as well as the submandibular glands. Massive infiltration of IgG4-expressing plasma cells was observed in testis and prostate tissues. Serum concentrations of B cell activating factor belonging to the tumor necrosis factor family (BAFF) were elevated in parallel with serum IgG4 concentrations, and infiltration of BAFF-receptor (BAFF-R)-expressing B cells and BAFF-expressing lymphoid cells was observed around the ectopic lymphoid foci in the affected urogenital tissues. To date, testicular involvement in a patient diagnosed with IgG4-RD had not been reported, making this the first reported case of IgG4-related epididymo-orchitis. These findings suggest that the immune mechanism underlying ectopic lymphoneogenesis in IgG4-RD may involve enhanced BAFF/BAFF-R interactions among lymphoid cells.